Bulkhead dilemma

[DaveW]

Hello,

While I've kept aquariums for quite a while, I recently upped the ante with a 112 gallon starfire that is bottom-drilled for a Herbie drain (3 holes for sch 40 1" pipe). I've never installed sump plumbing but have read all about it. However, I'm still a little nervous about having three holes drilled into the bottom of my tank.

Just for background info the tank bottom is resting on a mat, which is resting on a 3/4" plywood top that is supported by a steel frame. I made sure the top was perfectly level by using wood bondo and sanding it smooth and level. All is good so far. Next, in order to provide as much support to the glass around the 3 holes in the bottom (I've read that is a weak point in an aquarium), I left the plywood top directly beneath the area with the holes intact and merely drilled 3 holes in the top that line up with the holes in the aquarium bottom.

So, here's my question - am I going to have problems getting a water-tight seal on the bulkheads since the nut is tightening against the plywood instead of directly against the glass on the under-side of the tank? The bulkhead flange and gasket are both on the water side of the tank (inside the overflow) and the nut snugs up against the plywood that is directly under the area where the three holes in the tank are drilled. I reasoned that it should work since the gasket is in the correct place and that if the nut is tightened enough there will be enough pressure on the whole thing to keep water out. I've got them installed and have a little drip out of one. I think its because I might have over-tightened it to snug it all up (BH flange, gasket, glass bottom, mat, plywood, BH nut). Or it's possibly just a poorly designed install.

Maybe I don't need all that support for the glass around the 3 holes and would be better off cutting a big enough hole in the plywood bottom so that I can snug the bulkhead directly up to the glass under-side? The glass is 13mm thick so maybe it's strong enough?

Thanks in advance for helping me to benefit from your experience!

 

[laverda]

I have never heard of anyone doing it that way. Does not mean it will not work. The wood may compress over time allowing the bulkhead to loosen a little. If it gets wet the wood will swell and may do so unevenly.
Should decide to change it, the holes in the plywood need to large enough to get the nut on and to tighten it as well. That typically requires another 3/5 to 1” around the flange.
To be honest I don’t think it is worth the risk of trying it your way.

 

[blackizzz]

I would, personally, never put anything else than glass and gasket between the bulkhead.
Drill larger holes, and tighten the bulkheads directly on the glass.

It might work to do as you say, and it might not... But I wouldn't want 112 gallons of water on my floor and hours upon hours of work destroyed, would you? ;Drowning

 

[DaveW]

Good point about the wood compressing over time laverda, hadn’t thought of that.
Cutting out the hole sb easy enough after wrestling the tank off the stand (it seems awfully heavy for only 112 gallons.)
Blackizzz - exactly! I would be banned from the house if this thing leaks 112 gallons, better to do it correctly to start.
Thank you both!

 

[Billdogg]

What they said. The bulkhead MUST be a glass only sandwich. Regardless of the orientation of the bulkhead, the gasket MUST be on the flange side, not the side with the nut. Ideally, the gasket should be put on dry, but many (myself included) use a very small amount of silicone plumbers grease on it to help snug it down (just enough to make it shiny - no globs!).